1. Field of Invention
The present invention relates to a device for fitting a grinding wheel onto a grinding wheel spindle of the type which comprises an insert associated with the said grinding wheel and provided with threaded elements screwed onto threaded counter-elements provided in the said spindle.
The device of this invention can be applied with particular advantage to the fitting of a small diameter grinding wheel to the end of a corresponding grinding wheel spindle used for internal grinding operations.
2. Description of Prior Art
Because of the high precision required for grinding operations, whether for rough or finish grinding, the fitting of a grinding wheel onto a corresponding grinding wheel spindle must be effected in such a manner as to achieve a perfect positioning of the grinding wheel on the said grinding wheel spindle, so as to ensure the absence of axial and/or radial play between the grinding wheel and the grinding wheel spindle.
The aforementioned precision in the fitting is of even greater importance in the case of internal grinding operations, when the grinding wheel spindle is carried projecting from the shaft of the grinding machine. Moreover, taking into account the relatively frequent operations involving the changing of a worn grinding wheel for a new grinding wheel of identical characteristics, and likewise, taking into account the considerable daily output normally expected of a grinding machine, particularly when the latter is one in a continuous production line of finished parts, the aforementioned fitting must be effected in such a manner, that these grinding wheel changing operations, can be carried out both speedily and accurately.
At present, the fitting of a grinding wheel to the end of a corresponding grindng wheel spindle is essentially carried out in accordance with the following known methods.
A. The grinding wheel spindle is coaxially extended at one end, by a tang of equal or lesser diameter, with which it forms an annular ledge. On this tang and against the annular ledge, a first annular washer is mounted; the grinding wheel is fitted on this tang, with one of its faces resting on this said first washer. A second annular washer is then mounted on the said tang, so that it rests against the other face of the grinding wheel. Finally, on a length of the said tang and accessible from the upper face of the said grinding wheel, a tightening nut is screwed on so as to press with predetermined force against the said second washer.
A first disadvantage of this conventional method resides in the fact that whenever a worn grinding wheel is changed for a new one of identical characteristics, it is necessary to dismount four parts (one worn grinding wheel, two washers and a screw-nut) and subsequently to mount another four parts (a new grinding wheel, two washers and a tightening nut). In consequence, such a changing operation calls not only for personnel with a certain amount of training, but also involves a relatively long period of time during which the grinding machine cannot operate. Such a relatively long interruption, apart from constituting by itself, a technical and economic inconvenience, can at times, require the stopping of the entire production line, for example in cases when the aforementioned changing operation of the grinding wheel cannot suitably be carried out at the time when the need for such a change is notified.
A further technical disadvantage lies in the fact that during the mounting and dismounting of the grinding wheel onto and from the said grinding wheel spindle, the abrasive material of the grinding wheel is in frictional contact with the said tang, on which it exerts an abrasive action. As a result of this, after a certain number of changes, the external diameter of the said tang decreases relatively to its original diameter, with resulting play between the tang and the grinding wheel, which is inadmissible in view of the precision required from such grinding operations. In this case, it becomes necessary to change the grinding wheel spindle.
B. The grinding wheel carrier spindle is provided at one end with an internally threaded blind hole. In the grinding wheel, there is incorporated a metal insert which forms a threaded tang jutting out from one of the faces of the said grinding wheel, coaxially with the grinding wheel itself. The mounting of such a grinding wheel on the grinding wheel spindle is effected by screwing the said threaded tang into the threaded blind hole of the said spindle.
A disadvantage of this conventional method resides in the fact that the metal insert -- expensive to produce -- forms an integral part of the associated grinding wheel, and must be discarded whenever the worn grinding wheel is changed.
Another disadvantage lies in the fact that this metal insert is generally fixed in the hole of the associated grinding wheel, by means of an appropriate cement which does not always withstand the stresses caused by the strong torques to which a grinding wheel is subjected during a grinding operation.
In U.S. Pat. No. 3,364,630 there is disclosed a wheel mounting wherein an abrasive roll made of a deformable foamed resin has a mounting hole of polygonal shape through which extends a drive spindle of corresponding shape. However, the abrasive roll is not adapted to be screw threaded to the end of the spindle as disclosed by the applicant.
U.S. Pat. No. 1,162,970 also discloses a wheel mounting comprising a grinding wheel having a noncircular aperture and recessed surface into which is inserted and fixed a flanged noncircular metal bushing of corresponding shape. Unlike the applicant's device the bushing has a square hole which receives the internally threaded square end of a drive spindle having an integral flange that clamps against the flange of the bushing. A screw threaded into the end of the spindle has a large head which clamps the grinding wheel axially against the integral flange on the spindle.
Applicant's device differs from the prior art discussed above in that the applicant provides a precision internal grinding wheel mounting comprising an elastically deformable, threaded insert or bush of polygonal form that is simultaneously rotatable with the grinding wheel for rapid attachment to and removal from a threaded end portion of the spindle, eliminates both radial and axial play in the mounting and protects the threads on the spindle from abrasion. Also, applicant's device has one less part and clamps the wheel both radially and axially between surfaces of the insert and spindle.